Background: Since severe obesity in youth (BMI for age ?120th percentile) has been steadily increasing, intensive clinical intervention is necessitated, which is often delivered in specialized pediatric obesity clinics. Since the home environment and parental behavioral modeling are two of the strongest predictors of child weight loss during behavioral weight loss interventions, a family-based treatment approach is warranted. This strategy has been moderately successful in our existing, evidence-based pediatric weight management program (Brenner FIT), but since programs such as Brenner FIT rely on face-to-face delivery of programmatic elements, the dose delivered is limited by the time constraints experienced by families enrolled in treatment. Therefore, the purpose of this study is to refine and pilot a tailored, mobile (mHealth) component to augment an existing, evidence-based pediatric weight management program (Brenner FIT) to determine acceptability from a patient and clinical staff perspective, feasibility, and economic costs relative to the established weight management protocol alone [i.e., Brenner FIT vs. Brenner FIT + mHealth (Brenner mFIT)]. Primary Aim 1: Finalize an intervention for adolescent youth with obesity, consisting of podcasts/videos and electronic self-monitoring, to promote reduced caloric intake and increase physical activity. Primary Aim 2: Pilot the intervention in dyads (n = 40) recruited from a pediatric weight loss clinic, to establish acceptability and feasibility of the intervention relative to standard care (n = 40). Secondary Aim: To establish costs associated with development and implementation of mHealth components when delivered with the Brenner FIT program. Study design: For this project, we will randomize 80 youth with obesity (13 ? 18yrs) and a caregiver (dyads) to the Brenner FIT condition or the Brenner mFIT condition. All participants will complete baseline measures prior to randomization, and at three and six months. All youth participants will receive a commercially available activity monitor. Caregivers will receive podcasts with a story about a caregiver supporting weight loss in a child by providing healthy foods/activities for his/her family, including healthy eating and physical activity information. Children will receive animated videos that contain healthy eating and physical activity messaging, with an engaging story of a child losing weight. All participants will have access to a website and mobile apps where they will track weight, diet, and physical activity for themselves (youth) or their child (parents). Based on their reports of weight, eating, and physical activity, the messaging received from clinical staff by the families will be individually tailored to promote healthy behaviors and overcome perceived barriers. The proposed research is innovative in that it explicitly incorporates theory into the intervention and evaluation components of the project and builds upon an existing literature on mHealth interventions that use mobile technology.